The present invention relates to a coupling arrangement between a fluid reservoir and a main brake cylinder for a motor vehicle brake system, wherein on one of the components of fluid reservoir or main brake cylinder two coupling arms with one coupling aperture each are arranged, wherein on the other component of fluid reservoir or main brake cylinder a mounting portion with a receiving aperture is arranged, wherein the two coupling arms contact the mounting portion in such a way that in a mounted state the coupling apertures and the receiving aperture are aligned with each other along a common axis, wherein for coupling the mounting portion to the two coupling arms a coupling bolt is insertable into the coupling apertures and the receiving aperture and is fixable relative to at least one coupling arm or to the mounting portion, wherein the coupling bolt is configured with a cylindrical shank portion and at least one radially protruding detent projection.
Hydraulic motor vehicle brake systems, of the kind used in large numbers in modern automobile manufacture, are conventionally filled with brake fluid prior to installation. For the first filling the entire hydraulic motor vehicle brake system is initially evacuated and then the brake fluid is “injected” into the fluid reservoir in order to execute the filling rapidly and under considerable pressure into the fluid reservoir. During this process reaction forces arise between the main brake cylinder and the fluid reservoir and lead to a relative movement of these two components relative to one another. During operation vibrations moreover occur over the service life of the vehicle and likewise have an effect upon the connection between main brake cylinder and fluid reservoir. In order to prevent an unintentional detachment of these two components from one another they need to be coupled to one another by a coupling arrangement durably and with sufficient stability to withstand the previously described mechanical influences.
Such coupling arrangements are prior art. For example the genre-defining background art according to the document WO 2011/012398 A2 discloses such a coupling arrangement, in which the fluid reservoir and the main brake cylinder are coupled to one another by a detent bolt. The detent bolt is manufactured from plastics material and has on its outer circumferential surface detent projections, which during the assembly process are elastically deformed in order to produce a detent connection. It has however emerged that this solution calls for very precise manufacture of the detent bolt and that even slight non-conformance or ageing of the detent bolt may result in an unintentional detachment of the connection between fluid reservoir and main brake cylinder. If for example the detent projections are dimensioned too small, they do not fulfill their retaining function. If on the other hand the detent projections are dimensioned too large, this may lead during assembly not only to an elastic deformation but also to a plastic deformation of the detent projections, with the result that the detent bolt is damaged and so its retaining function is no longer guaranteed over the service life. In such cases even the above-mentioned filling process may already lead to an unintentional detachment of these two components from one another if the detent bolt is designed with insufficient precision or is of poor quality or has been damaged during assembly as a result of plastic deformation of the detent projections.
The document U.S. Pat. No. 7,441,408 B2 describes a similar coupling arrangement, in which a fastening bolt is likewise used. This is inserted completely into an undercut arrangement with coupling apertures and receiving aperture. The underlying problem of this solution is that, if the fastening bolt is not completely inserted, an incorrect assembly that is not immediately apparent may occur. As a result of the incorrect assembly the fluid reservoir may detach from the main brake cylinder. Disassembly is also relatively complex because the fastening bolt is disposed in a relatively hidden location.
Finally the document EP 1 190 923 B1 describes a coupling arrangement, in which a connection bolt with an angled end is used, which is then fixed by means of a detent receiver during assembly. This solution is unreliable because the connection bolt works loose relatively easily and may then become lost.